Electrical conductors of aluminum and methods for production of same



19, 1967 JEAN-LOUIS MERCIER 3, 41

ELECTRICAL CONDUCTORS OF ALUMINUM AND METHODS FOR PRODUCTION OF SAME Filed Feb. 18, 1964 HEAT TREATMENT UPON LEAVING WIRE COOLED IN AIR EXTRUSION DIE QOF BILLETS WITHOUT BILLEU HOMOGENIZED BILLETS HOMOGENIZED BILLETS HOMOGENIZED Sum TREATMENT ANDSLOWCRJLED AND COOLEDIN AIR AND SLOWCOOLED 6-11 d=3 =u d=3 d=11 =3 a=11 d= R R 9 R R 9 R R 9 R R Q mv EN TOR {,3 Jean -Louis MFICIQP United States Patent 3,359,141 ELECTRICAL CONDUCTORS OF ALUMINUM AND METHODS FOR PRODUCTION OF SAME Jean Louis Mercier, Issoire, Puy-de-Dome, France, as-

signor to Pechiney, Compagnie de Produits Chimiques et Electrometallurgiques, Paris, France Filed Feb. 18, 1964, Ser. No. 345,646 15 Claims. (Cl. 148-115) This invention relates to Wires formed of aluminum and more particularly to the improvement in the electrical conductivity and mechanical properties of such aluminum wires and methods of accomplishing same.

It is known that aluminum has excellent electrical conductivity but its use for electrically conductive wires is inhibited by poor mechanical properties. The mechanical properties can be improved by alloying the aluminum with other metals but such alloying with other metals operates materially to decrease the electrical conductivity. The industry has been content to comprise the situation by the formulation of a conductive aluminum alloy of the following composition, the alloy being referred to as conducting aluminum:

0.03% to 0.12% by weight silicon 0.01% to 0.45% by weight iron Remainder aluminum Electrically conductive aluminum alloy wires of the type described is normally fabricated by continuous casting of the alloy metal into billets of cylindrical shape and by subsequent conversion of such billets, as by drawing, to wire of the desired gauge.

It has been established by experience that increase in resistivity by a few percent can be achieved when the billet, prior to conversion, is subjected to a homogenization treatment, but loss is experienced in the breaking load.

It is an object of this invention to produce and to provide a method for producing electrically conductive aluminum wire of improved mechanical and electrical properties without experiencing the many disadvantages heretofore described, and it is a related object to provide a process for the fabrication of aluminum wire having improved electrical conductivity and mechanical properties wherein the homogenization treatment prior to conversion brings about additional lowering of electrical resistivity or increased electrical conductivity without substantial loss in breaking load. I

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, reference is made to the accompanying drawing in which the figure is a table of test results comparing wires produced in accordance wit-h the practice of this invention with wires of the type heretofore produced.

The concepts of this invention are embodied in the fabrication of aluminum wire having good electrical conductivity and good mechanical characteristics by the fabrication of the wire of conducting aluminum having from 0.01% to 0.05% by weight of copper as an alloying element therein; casting the alloy into billets; subjecting the cast billets to a homogenization step at a temperature above 400 C. and then converting the homogenized aluminum alloy billet into wire of a desired gauge after the homogenized billet has been gradually cooled in a furnace or in air. Best results are secured with an aluminum alloy that also contains silicon and iron as alloying elements in combination with the copper and wherein such alloying elements are present in an amount wherein the sum of silicon and copper is within the range of 0.09% to 0.07% by weight and the sum of the iron and copper is within the range of 0.3% to 0.35% by weight.

The time for homogenization can be varied but excellent results have been achieved by homogenization at the temperature described for eight or more hours.

The inventive concept can be illustrated by the following tests which are given by way of illustration, but not by way of limitation.

Castings were prepared of eight different compositions in which the elements alloyed with aluminum are set forth in the following table in which the amounts of alloying elements are given in percent by weight, the remainder of the composition comprising aluminum. In the formulations identified as F F and F the sum of the silicon plus copper is maintained substantially constant. In the formulations identified as S S and S the sum of the iron plus copper is held substantially constant, While in formulations C and C the silicon content i high.

TABLE I Reference Iron, Silicon, Copper, Impurities,

percent percent percent percent The copper which is identified as being present in the amount of 0.003% by weight in the castings of F and 5, might be considered as originating from impurities such that the castings containing the low amount of copper might be considered, for all practical purposes, as being free of copper.

Each of the alloy systems were separately melted, washed in a conventional manner, freed from slag and then cast into billets at a temperature of 750 C. The billets are formed by continuous casting to cylindrical shape having a diameter of mm. to enable drawing without being roughed.

The billets were cut to equal lengths of 250 mm. and subjected to the following program:

Four billets of each composition were selected with two of the four being selected from the head end of the castings and two from the tail end of the castings. Four other billets of each composition were homogenized for eight hours at 460 C. followed by slow cooling to 200 C. in the furnace. Two billets of each of the composi tions were homogenized for eight hours at 460 C. and then slowly cooled in air.

All of the billets were reheated to 350 C. and drawn at a speed of meters per minute to a diameter of 11 mm. When leaving the draw die, the temperature of the wire drawn from the billets which had not been homogenized was 470 C. While the temperature of the wire leaving the die was only 450 C. for the wire drawn from billets which had been homogenized, indicating that the latter were easier to draw. Of the four billets ho mogenized and then slowly cooled, two were drawn with cooling of the wire in air upon leaving the draw die while the other two were quenched in water.

About 15 meters of wire was secured from each billet. The samples that were used for testing were selected from the wire which did not include the first 1.5 meters. Four samples of wire obtained from billets which had been homogenized and eight samples of wire obtained from billets which had not been homogenized were worked and then further drawn down to a diameter of 3 mm.

The results are given in the table of the drawing in which: R is the breaking load in kg./mm. v is the electrical conductivity in ohms-cmP/cm. and has been calculated only for wires having a diameter of 3 mm.; d is the diameter of the wires in millimeters.

From the data set forth, it will be apparent that, in the absence of copper, the loss in breaking load by homogenization of the billet is considerable even when the wire is quenched after drawing. On the other hand, the breaking load is markedly reduced when the copper content reaches 0.05% by weight and the breaking load is practically cancelled out when the amount of copper reaches 0.025% by weight. It thus becomes possible to compensate for the decrease in breaking load which is secured by homogenization by a quench immediately following the drawing operation.

The variations in resitivity are of the same order in all cases and are balanced by a gain in conductivity on the order of 2% of the cold drawn Wire. On the other hand, when the billet is cooled in air following homogenization, more favorable breaking loads and less favorable resistivity are secured with increased silicon content.

Quenching immediately following the press provides for a slight gain in breaking load of the cold drawn wire with little, if any, loss in conductivity. Finally from the standpoint of conductivity in the annealed state, it is of interest to introduce copper while decreasing the silicon content by corresponding amounts.

The alloy composition of this invention may be set forth as follows, with the elements given in percent by weight:

Percent Iron 0.30 to 0.32 Silicon 0.05 to 0.06 Copper 0.015 to 0.035 Various impurities 0.02 Aluminum to make up to 100 The alloy composition above, after homogenization in air or with slow cooling, gives the following minimum characteristics:

Breaking loadgreater than 18 kg./mm.

Electrical resistivity-less than 2.776 microhrns/cm.

When drawing is followed immediately by quenching, the foregoing values are changes as follows:

Breaking load or resistancegreater than 18.5 kg/mm.

Electrical resistivity-less than 2.766 microhms/ cm.

In the foregoing description, hot drawing has been used for transformation of the billets to wires. It will be understood that the invention includes other means for transformation of the billets into wires such as by rolling, casting, extrusions and the like.

It will be understood that changes may be made in the details of formulation and operation without departing from the spirit of the invention, especially as defined in the following claims.

I claim:

1. In the production of electrically conductive aluminum wire, the steps of casting billets of aluminum containing copper as an alloying element in an amount within the range of 0.01% to 0.05% by weight, homogenizing the billets by heating to a temperature above 400 C. for at least 8 hours, slowly cooling the homogenized billets, and then reducing the billets to wire of the desired gauge.

2. The method as claimed in claim 1 in homogenized billets are cooled in open air.

3. The method as claimed in claim 1 in billets are reduced to wire by drawing.

4. The method as claimed in claim 3 in drawn wire is quenched in water.

5. The method as claimed in claim 3 in drawn wire is cooled in air.

6. In the production of electrically conductive aluminum wire, the steps of casting billets of aluminum containing copper and silicon as alloying elements and in which the which the which the which the which the copper is present in an amount within the range of 0.01% to 0.05% by weight and in which the sum of the copper and the silicon is within the range of 0.07% to 0.09% by weight, homogenizing the billets by heating to a temperature above 400 C., cooling the homogenized billets, and then reducing the billets to wire of the desired gauge.

7. In the production of electrically conductive aluminum wire, the steps of casting billets of aluminum containing copper and iron as alloying elements in which the copper is present in an amount within the range of 0.01% to 0.05% by weight and the sum of the copper and iron is Within the range of 0.03% to 0.35% by weight, homogenizing the billets by heating to a temperature above 400 C., cooling the homogenized billets, and then reducing the billets to wire of the desired gauge.

8. In the production of electrically conductive aluminum wire, the steps of casting billets of aluminum containing copper, silicon and iron as alloying elements in which the copper is present in an amount within the range of 0.01% to 0.05% by weight, the sum of copper and silicon is within the range of 0.07% to 0.09% by weight, and the sum of the copper and iron is within the range of 0.03% to 0.35% by weight, homogenizing the billets by heating to a temperature above 400 C., cooling the homogenized billets, and then reducing the billets to wire of the desired gauge.

9. The process as claimed in claim 8 in which the homogenization step is carried out by heating the billets at the elevated temperature for at least eight hours.

10. The process as claimed in claim 8 in which the homogenized billets are cooled immediately after homogenization by slow cooling in the furnace in which the homogenization step is carried out.

11. The process as claimed in claim 8 in which cooling following homogenization is carried out in the open air.

12. The process as claimed in claim 8 in which the reduction of billets to wire is carried out by drawing the billets for reduction through a draw die.

13. The process as claimed in claim 12 which includes the step of quenching the wire immediately following the drawing step.

14. The process as claimed in claim 12 which includes the step of cooling the wire in air immediately following the drawing step.

15. An electrical conductor formed of a composition in which the elements are present in percent by weight namely:

Iron 0.3 to 0.35 Silicon 0.05 to 0.06 Copper 0.015 to 0.035 Remainder-aluminum plus impurities.

References Cited UNITED STATES PATENTS 2,252,421 8/1941 Stroup -138 2,545,866 3/1951 Whitzel et a1. 75-138 X FOREIGN PATENTS' 610,824 10/ 1948 Great Britain.

OTHER REFERENCES Alloy Digest, A1-104, June 1961, 2 pages.

The Effect of Single Addition Metals on the Recrystallization, Electrical Conductivity and Rupture Strength of Pure Aluminum, Harrington, A.S.M. Nov. 15, 1948, pre print (pp. 1-3 relied on).

DAVID L. RECK, Primary Examiner. H. F. SAITO, W: W. STALLARD, Assistant Examiners. 

1. IN THE PRODUCTION OF ELECTRICALLY CONDUCTIVE ALUMINUM WIRE, THE STEPS OF CASTING BILLETS OF ALUMINUM CONTAINING COPPER AS AN ALLOYING ELEMENT IN AN AMOUNT WITHIN THE RANGE OF 0.01% TO 0.05% BY WEIGHT, HMOGENIZING THE BILLETS BY HEATING TO A TEMPERATURE ABOVE 400* C. FOR AT LEAST 8 HOURS, SLOWLY COOLING THE HOMOGENIZED BILLETS, AND THEN REDUCING THE BILLETS TO WIRE OF THE DESIRED GAUGE. 